iphone core data 基础操作

长平狐 发布于 2012/08/13 15:20
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1. 插入

AppDelegate *app = [[UIApplication sharedApplication] delegate];

NSManagedObjectContext *context = [app managedObjectContext];

NSManagedObject *newManagedObject = [NSEntityDescription insertNewObjectForEntityForName:@"entityname" inManagedObjectContext:context];

[newManagedObject setValue:value forKey:@"propertyname"];

NSError *error; if (![context save:&error]) {

// Handle the error…



NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSManagedObjectContext *managedObjectContext = appDelegate.managedObjectContext;
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Hero" inManagedObjectContext:managedObjectContext];
NSSortDescriptor *sortDescriptor1 = [[NSSortDescriptor alloc]
initWithKey:@”name” ascending:YES];
NSSortDescriptor *sortDescriptor2 = [[NSSortDescriptor alloc]
initWithKey:@”secretIdentity” ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc]
initWithObjects:sortDescriptor1, sortDescriptor2, nil];
[fetchRequest setSortDescriptors:sortDescriptors];
[fetchRequest setEntity:entity];
[fetchRequest setFetchBatchSize:20];
NSArray *objecs = [context executeFetchRequest: fetchRequest error:&error];


NSManagedObjectContext *managedObjectContext = appDelegate.managedObjectContext;

[context deleteObject:[objecs objectIndex:index];

// Save the context.

NSError *error; if (![context save:&error]) {

// Update to handle the error appropriately.

NSLog(@”Unresolved error %@, %@”, error, [error userInfo]);

exit(-1); // Fail



NSManagedObject *managedObject;

NSString *keypath;

NSString *labelString;

NSString *currentValue = [self.managedObject valueForKeyPath:self.keypath];

NSEntityDescription *ed = [self.managedObject entity];

NSDictionary *properties = [ed propertiesByName];

NSAttributeDescription *ad = [properties objectForKey:self.keypath];

NSString *defaultValue = nil;

if (ad != nil)

defaultValue = [ad defaultValue];

//core data relation  查询 或 修改

NSManagedObject *child = [NSEntityDescription insertNewObjectForEntityForName: @"Person" inManagedObjectContext:thePerson.managedObjectContext];

NSMutableSet *children = [person mutableSetValueForKey:@"children"]; //查询,可修改

[children addObject:child];

[children removeObject:childToBeRemoved];

[[children managedObjectContext] deleteObject:childToBeRemoved]; //真正的删除

NSSet *children = [person valueForKey:@"children"]; //查询,不可修改

for (NSManagedObject *oneChild in children) {

// do something



1 是否将图片存储到Core Data中,以及NSData如何存储的一些规则

First, always store your images in a usable format such as PNG or JPEG instead of NSData. This will save you a lot of headaches.

Second, the rule for storing binary data is:

  • < 100kb store in the same table as the relevant data
  • < 1mb store in a separate table attached via a relationship to avoid loading unnecessarily
  • > 1mb store on disk and reference it inside of Core Data

(1。图片尽量保存为文件 2。<100k 和相关数据保存在一张表中  <1M保存在单独的一张表中 >1M保存到磁盘文件)